Much interest and effort in recent years has been directed toward the development of solid state switches. Such switches would find numerous applications in modern technology where their advantages, as compared to other types of switches, of small size, high reliability, etc., can be fully exploited. For example, such switches could be advantageously used as cross-point switches in telecommunications systems.
Effort has been directed specifically toward the development of solid state switches capable of blocking high voltages and carrying large currents. For maximum versatility, such switches should be easily manufactured with other or similar switching devices on a common substrate. This should permit economies of manufacture and design flexibility.
A switch with such characteristics has been developed and is commonly referred to as a gated diode switch or GDS. This switch has a low impedance path in the ON or conducting state and a high impedance path in the OFF or blocking state. The switch can be easily fabricated in embodiments that will block voltages as large as 500 volts and carry currents larger than one ampere. Bilateral embodiments may be fabricated on a single chip with antiparallel connected switches.
Any of several methods may be used to control the current conduction state of the GDS. That is, several methods are available to change the switch from the ON state to the OFF state or vice versa. For example, either an opto-isolator or a metal oxide semiconductor (MOS) transistor in series with the GDS may be used to control the current conduction state. Light sensitive devices, e.g., a photodiode array, may also be used to control the current conduction state. Although perfectly adequate for many purposes, these methods have drawbacks for some applications.
When an opto-isolator is used, the maximum current capability of the switch is limited by the current handling capability of the opto-isolator. This is usually rather small and typically is only 0.5 amperes. When a metal oxide semiconductor transistor is used, a normally OFF device is connected in series with the normally ON GDS and the switch is therefore normally OFF. Photodiode arrays, because they produce only a small current when illuminated, are useful for switching a GDS only if the current through the GDS is very small, comparable to the photodiode array current, or for switching alternating currents. For some applications, these are undesirable features.